Embodiments of the present invention relate to imaging systems and particularly to cooperating light sources and detectors used in imaging systems.
The conventional imaging system includes an image reader having a light source for illuminating an original image to be read and a detector that provides a signal in response to a portion of the illumination that is received by the detector by reflection from the original image or by transmission through the original image. The signal may be used in an imaging system to make a printed copy. In such an imaging system having an image reader and an electrostatic print engine, a sheet of media is printed by the deposition of black toner in response to the signal. When the original image includes color text and graphics, the signal (and therefore the printed media) do not accurately convey a uniform grayscale rendering of the original colors.
A color copier of the type described in U.S. Pat. No. 5,105,267 typically uses xe2x80x9cwhitexe2x80x9d light from a halogen lamp to illuminate the original image. Such a copier detects reflected light by splitting the reflected light into three beams, filtering each beam through a primary color filter, and sensing each primary color intensity using a charge coupled device (CCD) sensor to provide three color-separated signals. Each color-separated signal is converted to digital form using an analog to digital converter (ADC). The three ADC outputs are coupled to a matrix multiply circuit that provides lightness and chroma signals, for example, signals L*, a*, and b* of a conventional constant-hue color space defined by the Commission Internationale de L""Éclairage (CIE).
The foregoing approach to providing a lightness signal involves circuit complexity and expensive components. Without the present invention, smaller and less costly imaging systems with lower power consumption and faster scanning rate would not be economically feasible.
Accordingly, an imaging system in one embodiment of the present invention includes an image reader having a light source and a detector. The light source illuminates the original image with an energy per unit area of the image. The energy includes a first quantity of a first color and a second quantity of a second color. The first and the second quantities are each proportional to a respective quantity of corresponding color of a reference point. The reference point is determined with reference to human vision. The detector responds to the illumination of the image by providing an electrical signal. The signal includes indicia of the image in accordance with an analog integration of the first quantity with the second quantity.
By illuminating the original image with light energy of more than one color and in quantities that correspond to human vision, the electrical signal provides indicia of the image with improved color correctness. Media that is printed by a monochrome printer responding to the signal has improved grayscale appearance.
When the signal, in one embodiment, is provided without a matrix multiplication circuit and without multiple ADCs, circuit complexity and related expenses are avoided.
In another embodiment, integrating the light energy of one color simultaneously with the light energy of a second color avoids the complexity and cost of a buffer memory. In such an embodiment, each analog to digital conversion result can be directly processed in pipeline fashion without buffer memory for accommodating subsequent processing that refers to more than one ADC result.
In yet another embodiment of the present invention, lower circuit complexity enables economical integrated circuit fabrication for both the light source control and detector signal processing functions on a single substrate.